//     Backbone.js 1.3.3

//     (c) 2010-2017 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://backbonejs.org

(function(factory) {
    
      // Establish the root object, `window` (`self`) in the browser, or `global` on the server.
      // We use `self` instead of `window` for `WebWorker` support.
      var root = (typeof self == 'object' && self.self === self && self) ||
                (typeof global == 'object' && global.global === global && global);
    
      // Set up Backbone appropriately for the environment. Start with AMD.
      if (typeof define === 'function' && define.amd) {
        define(['underscore', 'jquery', 'exports'], function(_, $, exports) {
          // Export global even in AMD case in case this script is loaded with
          // others that may still expect a global Backbone.
          root.Backbone = factory(root, exports, _, $);
        });
    
      // Next for Node.js or CommonJS. jQuery may not be needed as a module.
      } else if (typeof exports !== 'undefined') {
        var _ = require('underscore'), $;
        try { $ = require('jquery'); } catch (e) {}
        factory(root, exports, _, $);
    
      // Finally, as a browser global.
      } else {
        root.Backbone = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender || root.$));
      }
    
    })(function(root, Backbone, _, $) {
    
      // Initial Setup
      // -------------
    
      // Save the previous value of the `Backbone` variable, so that it can be
      // restored later on, if `noConflict` is used.
      var previousBackbone = root.Backbone;
    
      // Create a local reference to a common array method we'll want to use later.
      var slice = Array.prototype.slice;
    
      // Current version of the library. Keep in sync with `package.json`.
      Backbone.VERSION = '1.3.3';
    
      // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
      // the `$` variable.
      Backbone.$ = $;
    
      // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
      // to its previous owner. Returns a reference to this Backbone object.
      Backbone.noConflict = function() {
        root.Backbone = previousBackbone;
        return this;
      };
    
      // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
      // will fake `"PATCH"`, `"PUT"` and `"DELETE"` requests via the `_method` parameter and
      // set a `X-Http-Method-Override` header.
      Backbone.emulateHTTP = false;
    
      // Turn on `emulateJSON` to support legacy servers that can't deal with direct
      // `application/json` requests ... this will encode the body as
      // `application/x-www-form-urlencoded` instead and will send the model in a
      // form param named `model`.
      Backbone.emulateJSON = false;
    
      // Backbone.Events
      // ---------------
    
      // A module that can be mixed in to *any object* in order to provide it with
      // a custom event channel. You may bind a callback to an event with `on` or
      // remove with `off`; `trigger`-ing an event fires all callbacks in
      // succession.
      //
      //     var object = {};
      //     _.extend(object, Backbone.Events);
      //     object.on('expand', function(){ alert('expanded'); });
      //     object.trigger('expand');
      //
      var Events = Backbone.Events = {};
    
      // Regular expression used to split event strings.
      var eventSplitter = /\s+/;
    
      // A private global variable to share between listeners and listenees.
      var _listening;
    
      // Iterates over the standard `event, callback` (as well as the fancy multiple
      // space-separated events `"change blur", callback` and jQuery-style event
      // maps `{event: callback}`).
      var eventsApi = function(iteratee, events, name, callback, opts) {
        var i = 0, names;
        if (name && typeof name === 'object') {
          // Handle event maps.
          if (callback !== void 0 && 'context' in opts && opts.context === void 0) opts.context = callback;
          for (names = _.keys(name); i < names.length ; i++) {
            events = eventsApi(iteratee, events, names[i], name[names[i]], opts);
          }
        } else if (name && eventSplitter.test(name)) {
          // Handle space-separated event names by delegating them individually.
          for (names = name.split(eventSplitter); i < names.length; i++) {
            events = iteratee(events, names[i], callback, opts);
          }
        } else {
          // Finally, standard events.
          events = iteratee(events, name, callback, opts);
        }
        return events;
      };
    
      // Bind an event to a `callback` function. Passing `"all"` will bind
      // the callback to all events fired.
      Events.on = function(name, callback, context) {
        this._events = eventsApi(onApi, this._events || {}, name, callback, {
          context: context,
          ctx: this,
          listening: _listening
        });
    
        if (_listening) {
          var listeners = this._listeners || (this._listeners = {});
          listeners[_listening.id] = _listening;
          // Allow the listening to use a counter, instead of tracking
          // callbacks for library interop
          _listening.interop = false;
        }
    
        return this;
      };
    
      // Inversion-of-control versions of `on`. Tell *this* object to listen to
      // an event in another object... keeping track of what it's listening to
      // for easier unbinding later.
      Events.listenTo = function(obj, name, callback) {
        if (!obj) return this;
        var id = obj._listenId || (obj._listenId = _.uniqueId('l'));
        var listeningTo = this._listeningTo || (this._listeningTo = {});
        var listening = _listening = listeningTo[id];
    
        // This object is not listening to any other events on `obj` yet.
        // Setup the necessary references to track the listening callbacks.
        if (!listening) {
          this._listenId || (this._listenId = _.uniqueId('l'));
          listening = _listening = listeningTo[id] = new Listening(this, obj);
        }
    
        // Bind callbacks on obj.
        var error = tryCatchOn(obj, name, callback, this);
        _listening = void 0;
    
        if (error) throw error;
        // If the target obj is not Backbone.Events, track events manually.
        if (listening.interop) listening.on(name, callback);
    
        return this;
      };
    
      // The reducing API that adds a callback to the `events` object.
      var onApi = function(events, name, callback, options) {
        if (callback) {
          var handlers = events[name] || (events[name] = []);
          var context = options.context, ctx = options.ctx, listening = options.listening;
          if (listening) listening.count++;
    
          handlers.push({callback: callback, context: context, ctx: context || ctx, listening: listening});
        }
        return events;
      };
    
      // An try-catch guarded #on function, to prevent poisoning the global
      // `_listening` variable.
      var tryCatchOn = function(obj, name, callback, context) {
        try {
          obj.on(name, callback, context);
        } catch (e) {
          return e;
        }
      };
    
      // Remove one or many callbacks. If `context` is null, removes all
      // callbacks with that function. If `callback` is null, removes all
      // callbacks for the event. If `name` is null, removes all bound
      // callbacks for all events.
      Events.off = function(name, callback, context) {
        if (!this._events) return this;
        this._events = eventsApi(offApi, this._events, name, callback, {
          context: context,
          listeners: this._listeners
        });
    
        return this;
      };
    
      // Tell this object to stop listening to either specific events ... or
      // to every object it's currently listening to.
      Events.stopListening = function(obj, name, callback) {
        var listeningTo = this._listeningTo;
        if (!listeningTo) return this;
    
        var ids = obj ? [obj._listenId] : _.keys(listeningTo);
        for (var i = 0; i < ids.length; i++) {
          var listening = listeningTo[ids[i]];
    
          // If listening doesn't exist, this object is not currently
          // listening to obj. Break out early.
          if (!listening) break;
    
          listening.obj.off(name, callback, this);
          if (listening.interop) listening.off(name, callback);
        }
        if (_.isEmpty(listeningTo)) this._listeningTo = void 0;
    
        return this;
      };
    
      // The reducing API that removes a callback from the `events` object.
      var offApi = function(events, name, callback, options) {
        if (!events) return;
    
        var context = options.context, listeners = options.listeners;
        var i = 0, names;
    
        // Delete all event listeners and "drop" events.
        if (!name && !context && !callback) {
          for (names = _.keys(listeners); i < names.length; i++) {
            listeners[names[i]].cleanup();
          }
          return;
        }
    
        names = name ? [name] : _.keys(events);
        for (; i < names.length; i++) {
          name = names[i];
          var handlers = events[name];
    
          // Bail out if there are no events stored.
          if (!handlers) break;
    
          // Find any remaining events.
          var remaining = [];
          for (var j = 0; j < handlers.length; j++) {
            var handler = handlers[j];
            if (
              callback && callback !== handler.callback &&
                callback !== handler.callback._callback ||
                  context && context !== handler.context
            ) {
              remaining.push(handler);
            } else {
              var listening = handler.listening;
              if (listening) listening.off(name, callback);
            }
          }
    
          // Replace events if there are any remaining.  Otherwise, clean up.
          if (remaining.length) {
            events[name] = remaining;
          } else {
            delete events[name];
          }
        }
    
        return events;
      };
    
      // Bind an event to only be triggered a single time. After the first time
      // the callback is invoked, its listener will be removed. If multiple events
      // are passed in using the space-separated syntax, the handler will fire
      // once for each event, not once for a combination of all events.
      Events.once = function(name, callback, context) {
        // Map the event into a `{event: once}` object.
        var events = eventsApi(onceMap, {}, name, callback, this.off.bind(this));
        if (typeof name === 'string' && context == null) callback = void 0;
        return this.on(events, callback, context);
      };
    
      // Inversion-of-control versions of `once`.
      Events.listenToOnce = function(obj, name, callback) {
        // Map the event into a `{event: once}` object.
        var events = eventsApi(onceMap, {}, name, callback, this.stopListening.bind(this, obj));
        return this.listenTo(obj, events);
      };
    
      // Reduces the event callbacks into a map of `{event: onceWrapper}`.
      // `offer` unbinds the `onceWrapper` after it has been called.
      var onceMap = function(map, name, callback, offer) {
        if (callback) {
          var once = map[name] = _.once(function() {
            offer(name, once);
            callback.apply(this, arguments);
          });
          once._callback = callback;
        }
        return map;
      };
    
      // Trigger one or many events, firing all bound callbacks. Callbacks are
      // passed the same arguments as `trigger` is, apart from the event name
      // (unless you're listening on `"all"`, which will cause your callback to
      // receive the true name of the event as the first argument).
      Events.trigger = function(name) {
        if (!this._events) return this;
    
        var length = Math.max(0, arguments.length - 1);
        var args = Array(length);
        for (var i = 0; i < length; i++) args[i] = arguments[i + 1];
    
        eventsApi(triggerApi, this._events, name, void 0, args);
        return this;
      };
    
      // Handles triggering the appropriate event callbacks.
      var triggerApi = function(objEvents, name, callback, args) {
        if (objEvents) {
          var events = objEvents[name];
          var allEvents = objEvents.all;
          if (events && allEvents) allEvents = allEvents.slice();
          if (events) triggerEvents(events, args);
          if (allEvents) triggerEvents(allEvents, [name].concat(args));
        }
        return objEvents;
      };
    
      // A difficult-to-believe, but optimized internal dispatch function for
      // triggering events. Tries to keep the usual cases speedy (most internal
      // Backbone events have 3 arguments).
      var triggerEvents = function(events, args) {
        var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];
        switch (args.length) {
          case 0: while (++i < l) (ev = events[i]).callback.call(ev.ctx); return;
          case 1: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1); return;
          case 2: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2); return;
          case 3: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3); return;
          default: while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args); return;
        }
      };
    
      // A listening class that tracks and cleans up memory bindings
      // when all callbacks have been offed.
      var Listening = function(listener, obj) {
        this.id = listener._listenId;
        this.listener = listener;
        this.obj = obj;
        this.interop = true;
        this.count = 0;
        this._events = void 0;
      };
    
      Listening.prototype.on = Events.on;
    
      // Offs a callback (or several).
      // Uses an optimized counter if the listenee uses Backbone.Events.
      // Otherwise, falls back to manual tracking to support events
      // library interop.
      Listening.prototype.off = function(name, callback) {
        var cleanup;
        if (this.interop) {
          this._events = eventsApi(offApi, this._events, name, callback, {
            context: void 0,
            listeners: void 0
          });
          cleanup = !this._events;
        } else {
          this.count--;
          cleanup = this.count === 0;
        }
        if (cleanup) this.cleanup();
      };
    
      // Cleans up memory bindings between the listener and the listenee.
      Listening.prototype.cleanup = function() {
        delete this.listener._listeningTo[this.obj._listenId];
        if (!this.interop) delete this.obj._listeners[this.id];
      };
    
      // Aliases for backwards compatibility.
      Events.bind   = Events.on;
      Events.unbind = Events.off;
    
      // Allow the `Backbone` object to serve as a global event bus, for folks who
      // want global "pubsub" in a convenient place.
      _.extend(Backbone, Events);
    
      // Backbone.Model
      // --------------
    
      // Backbone **Models** are the basic data object in the framework --
      // frequently representing a row in a table in a database on your server.
      // A discrete chunk of data and a bunch of useful, related methods for
      // performing computations and transformations on that data.
    
      // Create a new model with the specified attributes. A client id (`cid`)
      // is automatically generated and assigned for you.
      var Model = Backbone.Model = function(attributes, options) {
        var attrs = attributes || {};
        options || (options = {});
        this.preinitialize.apply(this, arguments);
        this.cid = _.uniqueId(this.cidPrefix);
        this.attributes = {};
        if (options.collection) this.collection = options.collection;
        if (options.parse) attrs = this.parse(attrs, options) || {};
        var defaults = _.result(this, 'defaults');
        attrs = _.defaults(_.extend({}, defaults, attrs), defaults);
        this.set(attrs, options);
        this.changed = {};
        this.initialize.apply(this, arguments);
      };
    
      // Attach all inheritable methods to the Model prototype.
      _.extend(Model.prototype, Events, {
    
        // A hash of attributes whose current and previous value differ.
        changed: null,
    
        // The value returned during the last failed validation.
        validationError: null,
    
        // The default name for the JSON `id` attribute is `"id"`. MongoDB and
        // CouchDB users may want to set this to `"_id"`.
        idAttribute: 'id',
    
        // The prefix is used to create the client id which is used to identify models locally.
        // You may want to override this if you're experiencing name clashes with model ids.
        cidPrefix: 'c',
    
        // preinitialize is an empty function by default. You can override it with a function
        // or object.  preinitialize will run before any instantiation logic is run in the Model.
        preinitialize: function(){},
    
        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},
    
        // Return a copy of the model's `attributes` object.
        toJSON: function(options) {
          return _.clone(this.attributes);
        },
    
        // Proxy `Backbone.sync` by default -- but override this if you need
        // custom syncing semantics for *this* particular model.
        sync: function() {
          return Backbone.sync.apply(this, arguments);
        },
    
        // Get the value of an attribute.
        get: function(attr) {
          return this.attributes[attr];
        },
    
        // Get the HTML-escaped value of an attribute.
        escape: function(attr) {
          return _.escape(this.get(attr));
        },
    
        // Returns `true` if the attribute contains a value that is not null
        // or undefined.
        has: function(attr) {
          return this.get(attr) != null;
        },
    
        // Special-cased proxy to underscore's `_.matches` method.
        matches: function(attrs) {
          return !!_.iteratee(attrs, this)(this.attributes);
        },
    
        // Set a hash of model attributes on the object, firing `"change"`. This is
        // the core primitive operation of a model, updating the data and notifying
        // anyone who needs to know about the change in state. The heart of the beast.
        set: function(key, val, options) {
          if (key == null) return this;
    
          // Handle both `"key", value` and `{key: value}` -style arguments.
          var attrs;
          if (typeof key === 'object') {
            attrs = key;
            options = val;
          } else {
            (attrs = {})[key] = val;
          }
    
          options || (options = {});
    
          // Run validation.
          if (!this._validate(attrs, options)) return false;
    
          // Extract attributes and options.
          var unset      = options.unset;
          var silent     = options.silent;
          var changes    = [];
          var changing   = this._changing;
          this._changing = true;
    
          if (!changing) {
            this._previousAttributes = _.clone(this.attributes);
            this.changed = {};
          }
    
          var current = this.attributes;
          var changed = this.changed;
          var prev    = this._previousAttributes;
    
          // For each `set` attribute, update or delete the current value.
          for (var attr in attrs) {
            val = attrs[attr];
            if (!_.isEqual(current[attr], val)) changes.push(attr);
            if (!_.isEqual(prev[attr], val)) {
              changed[attr] = val;
            } else {
              delete changed[attr];
            }
            unset ? delete current[attr] : current[attr] = val;
          }
    
          // Update the `id`.
          if (this.idAttribute in attrs) this.id = this.get(this.idAttribute);
    
          // Trigger all relevant attribute changes.
          if (!silent) {
            if (changes.length) this._pending = options;
            for (var i = 0; i < changes.length; i++) {
              this.trigger('change:' + changes[i], this, current[changes[i]], options);
            }
          }
    
          // You might be wondering why there's a `while` loop here. Changes can
          // be recursively nested within `"change"` events.
          if (changing) return this;
          if (!silent) {
            while (this._pending) {
              options = this._pending;
              this._pending = false;
              this.trigger('change', this, options);
            }
          }
          this._pending = false;
          this._changing = false;
          return this;
        },
    
        // Remove an attribute from the model, firing `"change"`. `unset` is a noop
        // if the attribute doesn't exist.
        unset: function(attr, options) {
          return this.set(attr, void 0, _.extend({}, options, {unset: true}));
        },
    
        // Clear all attributes on the model, firing `"change"`.
        clear: function(options) {
          var attrs = {};
          for (var key in this.attributes) attrs[key] = void 0;
          return this.set(attrs, _.extend({}, options, {unset: true}));
        },
    
        // Determine if the model has changed since the last `"change"` event.
        // If you specify an attribute name, determine if that attribute has changed.
        hasChanged: function(attr) {
          if (attr == null) return !_.isEmpty(this.changed);
          return _.has(this.changed, attr);
        },
    
        // Return an object containing all the attributes that have changed, or
        // false if there are no changed attributes. Useful for determining what
        // parts of a view need to be updated and/or what attributes need to be
        // persisted to the server. Unset attributes will be set to undefined.
        // You can also pass an attributes object to diff against the model,
        // determining if there *would be* a change.
        changedAttributes: function(diff) {
          if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
          var old = this._changing ? this._previousAttributes : this.attributes;
          var changed = {};
          var hasChanged;
          for (var attr in diff) {
            var val = diff[attr];
            if (_.isEqual(old[attr], val)) continue;
            changed[attr] = val;
            hasChanged = true;
          }
          return hasChanged ? changed : false;
        },
    
        // Get the previous value of an attribute, recorded at the time the last
        // `"change"` event was fired.
        previous: function(attr) {
          if (attr == null || !this._previousAttributes) return null;
          return this._previousAttributes[attr];
        },
    
        // Get all of the attributes of the model at the time of the previous
        // `"change"` event.
        previousAttributes: function() {
          return _.clone(this._previousAttributes);
        },
    
        // Fetch the model from the server, merging the response with the model's
        // local attributes. Any changed attributes will trigger a "change" event.
        fetch: function(options) {
          options = _.extend({parse: true}, options);
          var model = this;
          var success = options.success;
          options.success = function(resp) {
            var serverAttrs = options.parse ? model.parse(resp, options) : resp;
            if (!model.set(serverAttrs, options)) return false;
            if (success) success.call(options.context, model, resp, options);
            model.trigger('sync', model, resp, options);
          };
          wrapError(this, options);
          return this.sync('read', this, options);
        },
    
        // Set a hash of model attributes, and sync the model to the server.
        // If the server returns an attributes hash that differs, the model's
        // state will be `set` again.
        save: function(key, val, options) {
          // Handle both `"key", value` and `{key: value}` -style arguments.
          var attrs;
          if (key == null || typeof key === 'object') {
            attrs = key;
            options = val;
          } else {
            (attrs = {})[key] = val;
          }
    
          options = _.extend({validate: true, parse: true}, options);
          var wait = options.wait;
    
          // If we're not waiting and attributes exist, save acts as
          // `set(attr).save(null, opts)` with validation. Otherwise, check if
          // the model will be valid when the attributes, if any, are set.
          if (attrs && !wait) {
            if (!this.set(attrs, options)) return false;
          } else if (!this._validate(attrs, options)) {
            return false;
          }
    
          // After a successful server-side save, the client is (optionally)
          // updated with the server-side state.
          var model = this;
          var success = options.success;
          var attributes = this.attributes;
          options.success = function(resp) {
            // Ensure attributes are restored during synchronous saves.
            model.attributes = attributes;
            var serverAttrs = options.parse ? model.parse(resp, options) : resp;
            if (wait) serverAttrs = _.extend({}, attrs, serverAttrs);
            if (serverAttrs && !model.set(serverAttrs, options)) return false;
            if (success) success.call(options.context, model, resp, options);
            model.trigger('sync', model, resp, options);
          };
          wrapError(this, options);
    
          // Set temporary attributes if `{wait: true}` to properly find new ids.
          if (attrs && wait) this.attributes = _.extend({}, attributes, attrs);
    
          var method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');
          if (method === 'patch' && !options.attrs) options.attrs = attrs;
          var xhr = this.sync(method, this, options);
    
          // Restore attributes.
          this.attributes = attributes;
    
          return xhr;
        },
    
        // Destroy this model on the server if it was already persisted.
        // Optimistically removes the model from its collection, if it has one.
        // If `wait: true` is passed, waits for the server to respond before removal.
        destroy: function(options) {
          options = options ? _.clone(options) : {};
          var model = this;
          var success = options.success;
          var wait = options.wait;
    
          var destroy = function() {
            model.stopListening();
            model.trigger('destroy', model, model.collection, options);
          };
    
          options.success = function(resp) {
            if (wait) destroy();
            if (success) success.call(options.context, model, resp, options);
            if (!model.isNew()) model.trigger('sync', model, resp, options);
          };
    
          var xhr = false;
          if (this.isNew()) {
            _.defer(options.success);
          } else {
            wrapError(this, options);
            xhr = this.sync('delete', this, options);
          }
          if (!wait) destroy();
          return xhr;
        },
    
        // Default URL for the model's representation on the server -- if you're
        // using Backbone's restful methods, override this to change the endpoint
        // that will be called.
        url: function() {
          var base =
            _.result(this, 'urlRoot') ||
            _.result(this.collection, 'url') ||
            urlError();
          if (this.isNew()) return base;
          var id = this.get(this.idAttribute);
          return base.replace(/[^\/]$/, '$&/') + encodeURIComponent(id);
        },
    
        // **parse** converts a response into the hash of attributes to be `set` on
        // the model. The default implementation is just to pass the response along.
        parse: function(resp, options) {
          return resp;
        },
    
        // Create a new model with identical attributes to this one.
        clone: function() {
          return new this.constructor(this.attributes);
        },
    
        // A model is new if it has never been saved to the server, and lacks an id.
        isNew: function() {
          return !this.has(this.idAttribute);
        },
    
        // Check if the model is currently in a valid state.
        isValid: function(options) {
          return this._validate({}, _.extend({}, options, {validate: true}));
        },
    
        // Run validation against the next complete set of model attributes,
        // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
        _validate: function(attrs, options) {
          if (!options.validate || !this.validate) return true;
          attrs = _.extend({}, this.attributes, attrs);
          var error = this.validationError = this.validate(attrs, options) || null;
          if (!error) return true;
          this.trigger('invalid', this, error, _.extend(options, {validationError: error}));
          return false;
        }
    
      });
    
      // Backbone.Collection
      // -------------------
    
      // If models tend to represent a single row of data, a Backbone Collection is
      // more analogous to a table full of data ... or a small slice or page of that
      // table, or a collection of rows that belong together for a particular reason
      // -- all of the messages in this particular folder, all of the documents
      // belonging to this particular author, and so on. Collections maintain
      // indexes of their models, both in order, and for lookup by `id`.
    
      // Create a new **Collection**, perhaps to contain a specific type of `model`.
      // If a `comparator` is specified, the Collection will maintain
      // its models in sort order, as they're added and removed.
      var Collection = Backbone.Collection = function(models, options) {
        options || (options = {});
        this.preinitialize.apply(this, arguments);
        if (options.model) this.model = options.model;
        if (options.comparator !== void 0) this.comparator = options.comparator;
        this._reset();
        this.initialize.apply(this, arguments);
        if (models) this.reset(models, _.extend({silent: true}, options));
      };
    
      // Default options for `Collection#set`.
      var setOptions = {add: true, remove: true, merge: true};
      var addOptions = {add: true, remove: false};
    
      // Splices `insert` into `array` at index `at`.
      var splice = function(array, insert, at) {
        at = Math.min(Math.max(at, 0), array.length);
        var tail = Array(array.length - at);
        var length = insert.length;
        var i;
        for (i = 0; i < tail.length; i++) tail[i] = array[i + at];
        for (i = 0; i < length; i++) array[i + at] = insert[i];
        for (i = 0; i < tail.length; i++) array[i + length + at] = tail[i];
      };
    
      // Define the Collection's inheritable methods.
      _.extend(Collection.prototype, Events, {
    
        // The default model for a collection is just a **Backbone.Model**.
        // This should be overridden in most cases.
        model: Model,
    
    
        // preinitialize is an empty function by default. You can override it with a function
        // or object.  preinitialize will run before any instantiation logic is run in the Collection.
        preinitialize: function(){},
    
        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},
    
        // The JSON representation of a Collection is an array of the
        // models' attributes.
        toJSON: function(options) {
          return this.map(function(model) { return model.toJSON(options); });
        },
    
        // Proxy `Backbone.sync` by default.
        sync: function() {
          return Backbone.sync.apply(this, arguments);
        },
    
        // Add a model, or list of models to the set. `models` may be Backbone
        // Models or raw JavaScript objects to be converted to Models, or any
        // combination of the two.
        add: function(models, options) {
          return this.set(models, _.extend({merge: false}, options, addOptions));
        },
    
        // Remove a model, or a list of models from the set.
        remove: function(models, options) {
          options = _.extend({}, options);
          var singular = !_.isArray(models);
          models = singular ? [models] : models.slice();
          var removed = this._removeModels(models, options);
          if (!options.silent && removed.length) {
            options.changes = {added: [], merged: [], removed: removed};
            this.trigger('update', this, options);
          }
          return singular ? removed[0] : removed;
        },
    
        // Update a collection by `set`-ing a new list of models, adding new ones,
        // removing models that are no longer present, and merging models that
        // already exist in the collection, as necessary. Similar to **Model#set**,
        // the core operation for updating the data contained by the collection.
        set: function(models, options) {
          if (models == null) return;
    
          options = _.extend({}, setOptions, options);
          if (options.parse && !this._isModel(models)) {
            models = this.parse(models, options) || [];
          }
    
          var singular = !_.isArray(models);
          models = singular ? [models] : models.slice();
    
          var at = options.at;
          if (at != null) at = +at;
          if (at > this.length) at = this.length;
          if (at < 0) at += this.length + 1;
    
          var set = [];
          var toAdd = [];
          var toMerge = [];
          var toRemove = [];
          var modelMap = {};
    
          var add = options.add;
          var merge = options.merge;
          var remove = options.remove;
    
          var sort = false;
          var sortable = this.comparator && at == null && options.sort !== false;
          var sortAttr = _.isString(this.comparator) ? this.comparator : null;
    
          // Turn bare objects into model references, and prevent invalid models
          // from being added.
          var model, i;
          for (i = 0; i < models.length; i++) {
            model = models[i];
    
            // If a duplicate is found, prevent it from being added and
            // optionally merge it into the existing model.
            var existing = this.get(model);
            if (existing) {
              if (merge && model !== existing) {
                var attrs = this._isModel(model) ? model.attributes : model;
                if (options.parse) attrs = existing.parse(attrs, options);
                existing.set(attrs, options);
                toMerge.push(existing);
                if (sortable && !sort) sort = existing.hasChanged(sortAttr);
              }
              if (!modelMap[existing.cid]) {
                modelMap[existing.cid] = true;
                set.push(existing);
              }
              models[i] = existing;
    
            // If this is a new, valid model, push it to the `toAdd` list.
            } else if (add) {
              model = models[i] = this._prepareModel(model, options);
              if (model) {
                toAdd.push(model);
                this._addReference(model, options);
                modelMap[model.cid] = true;
                set.push(model);
              }
            }
          }
    
          // Remove stale models.
          if (remove) {
            for (i = 0; i < this.length; i++) {
              model = this.models[i];
              if (!modelMap[model.cid]) toRemove.push(model);
            }
            if (toRemove.length) this._removeModels(toRemove, options);
          }
    
          // See if sorting is needed, update `length` and splice in new models.
          var orderChanged = false;
          var replace = !sortable && add && remove;
          if (set.length && replace) {
            orderChanged = this.length !== set.length || _.some(this.models, function(m, index) {
              return m !== set[index];
            });
            this.models.length = 0;
            splice(this.models, set, 0);
            this.length = this.models.length;
          } else if (toAdd.length) {
            if (sortable) sort = true;
            splice(this.models, toAdd, at == null ? this.length : at);
            this.length = this.models.length;
          }
    
          // Silently sort the collection if appropriate.
          if (sort) this.sort({silent: true});
    
          // Unless silenced, it's time to fire all appropriate add/sort/update events.
          if (!options.silent) {
            for (i = 0; i < toAdd.length; i++) {
              if (at != null) options.index = at + i;
              model = toAdd[i];
              model.trigger('add', model, this, options);
            }
            if (sort || orderChanged) this.trigger('sort', this, options);
            if (toAdd.length || toRemove.length || toMerge.length) {
              options.changes = {
                added: toAdd,
                removed: toRemove,
                merged: toMerge
              };
              this.trigger('update', this, options);
            }
          }
    
          // Return the added (or merged) model (or models).
          return singular ? models[0] : models;
        },
    
        // When you have more items than you want to add or remove individually,
        // you can reset the entire set with a new list of models, without firing
        // any granular `add` or `remove` events. Fires `reset` when finished.
        // Useful for bulk operations and optimizations.
        reset: function(models, options) {
          options = options ? _.clone(options) : {};
          for (var i = 0; i < this.models.length; i++) {
            this._removeReference(this.models[i], options);
          }
          options.previousModels = this.models;
          this._reset();
          models = this.add(models, _.extend({silent: true}, options));
          if (!options.silent) this.trigger('reset', this, options);
          return models;
        },
    
        // Add a model to the end of the collection.
        push: function(model, options) {
          return this.add(model, _.extend({at: this.length}, options));
        },
    
        // Remove a model from the end of the collection.
        pop: function(options) {
          var model = this.at(this.length - 1);
          return this.remove(model, options);
        },
    
        // Add a model to the beginning of the collection.
        unshift: function(model, options) {
          return this.add(model, _.extend({at: 0}, options));
        },
    
        // Remove a model from the beginning of the collection.
        shift: function(options) {
          var model = this.at(0);
          return this.remove(model, options);
        },
    
        // Slice out a sub-array of models from the collection.
        slice: function() {
          return slice.apply(this.models, arguments);
        },
    
        // Get a model from the set by id, cid, model object with id or cid
        // properties, or an attributes object that is transformed through modelId.
        get: function(obj) {
          if (obj == null) return void 0;
          return this._byId[obj] ||
            this._byId[this.modelId(this._isModel(obj) ? obj.attributes : obj)] ||
            obj.cid && this._byId[obj.cid];
        },
    
        // Returns `true` if the model is in the collection.
        has: function(obj) {
          return this.get(obj) != null;
        },
    
        // Get the model at the given index.
        at: function(index) {
          if (index < 0) index += this.length;
          return this.models[index];
        },
    
        // Return models with matching attributes. Useful for simple cases of
        // `filter`.
        where: function(attrs, first) {
          return this[first ? 'find' : 'filter'](attrs);
        },
    
        // Return the first model with matching attributes. Useful for simple cases
        // of `find`.
        findWhere: function(attrs) {
          return this.where(attrs, true);
        },
    
        // Force the collection to re-sort itself. You don't need to call this under
        // normal circumstances, as the set will maintain sort order as each item
        // is added.
        sort: function(options) {
          var comparator = this.comparator;
          if (!comparator) throw new Error('Cannot sort a set without a comparator');
          options || (options = {});
    
          var length = comparator.length;
          if (_.isFunction(comparator)) comparator = comparator.bind(this);
    
          // Run sort based on type of `comparator`.
          if (length === 1 || _.isString(comparator)) {
            this.models = this.sortBy(comparator);
          } else {
            this.models.sort(comparator);
          }
          if (!options.silent) this.trigger('sort', this, options);
          return this;
        },
    
        // Pluck an attribute from each model in the collection.
        pluck: function(attr) {
          return this.map(attr + '');
        },
    
        // Fetch the default set of models for this collection, resetting the
        // collection when they arrive. If `reset: true` is passed, the response
        // data will be passed through the `reset` method instead of `set`.
        fetch: function(options) {
          options = _.extend({parse: true}, options);
          var success = options.success;
          var collection = this;
          options.success = function(resp) {
            var method = options.reset ? 'reset' : 'set';
            collection[method](resp, options);
            if (success) success.call(options.context, collection, resp, options);
            collection.trigger('sync', collection, resp, options);
          };
          wrapError(this, options);
          return this.sync('read', this, options);
        },
    
        // Create a new instance of a model in this collection. Add the model to the
        // collection immediately, unless `wait: true` is passed, in which case we
        // wait for the server to agree.
        create: function(model, options) {
          options = options ? _.clone(options) : {};
          var wait = options.wait;
          model = this._prepareModel(model, options);
          if (!model) return false;
          if (!wait) this.add(model, options);
          var collection = this;
          var success = options.success;
          options.success = function(m, resp, callbackOpts) {
            if (wait) collection.add(m, callbackOpts);
            if (success) success.call(callbackOpts.context, m, resp, callbackOpts);
          };
          model.save(null, options);
          return model;
        },
    
        // **parse** converts a response into a list of models to be added to the
        // collection. The default implementation is just to pass it through.
        parse: function(resp, options) {
          return resp;
        },
    
        // Create a new collection with an identical list of models as this one.
        clone: function() {
          return new this.constructor(this.models, {
            model: this.model,
            comparator: this.comparator
          });
        },
    
        // Define how to uniquely identify models in the collection.
        modelId: function(attrs) {
          return attrs[this.model.prototype.idAttribute || 'id'];
        },
    
        // Get an iterator of all models in this collection.
        values: function() {
          return new CollectionIterator(this, ITERATOR_VALUES);
        },
    
        // Get an iterator of all model IDs in this collection.
        keys: function() {
          return new CollectionIterator(this, ITERATOR_KEYS);
        },
    
        // Get an iterator of all [ID, model] tuples in this collection.
        entries: function() {
          return new CollectionIterator(this, ITERATOR_KEYSVALUES);
        },
    
        // Private method to reset all internal state. Called when the collection
        // is first initialized or reset.
        _reset: function() {
          this.length = 0;
          this.models = [];
          this._byId  = {};
        },
    
        // Prepare a hash of attributes (or other model) to be added to this
        // collection.
        _prepareModel: function(attrs, options) {
          if (this._isModel(attrs)) {
            if (!attrs.collection) attrs.collection = this;
            return attrs;
          }
          options = options ? _.clone(options) : {};
          options.collection = this;
          var model = new this.model(attrs, options);
          if (!model.validationError) return model;
          this.trigger('invalid', this, model.validationError, options);
          return false;
        },
    
        // Internal method called by both remove and set.
        _removeModels: function(models, options) {
          var removed = [];
          for (var i = 0; i < models.length; i++) {
            var model = this.get(models[i]);
            if (!model) continue;
    
            var index = this.indexOf(model);
            this.models.splice(index, 1);
            this.length--;
    
            // Remove references before triggering 'remove' event to prevent an
            // infinite loop. #3693
            delete this._byId[model.cid];
            var id = this.modelId(model.attributes);
            if (id != null) delete this._byId[id];
    
            if (!options.silent) {
              options.index = index;
              model.trigger('remove', model, this, options);
            }
    
            removed.push(model);
            this._removeReference(model, options);
          }
          return removed;
        },
    
        // Method for checking whether an object should be considered a model for
        // the purposes of adding to the collection.
        _isModel: function(model) {
          return model instanceof Model;
        },
    
        // Internal method to create a model's ties to a collection.
        _addReference: function(model, options) {
          this._byId[model.cid] = model;
          var id = this.modelId(model.attributes);
          if (id != null) this._byId[id] = model;
          model.on('all', this._onModelEvent, this);
        },
    
        // Internal method to sever a model's ties to a collection.
        _removeReference: function(model, options) {
          delete this._byId[model.cid];
          var id = this.modelId(model.attributes);
          if (id != null) delete this._byId[id];
          if (this === model.collection) delete model.collection;
          model.off('all', this._onModelEvent, this);
        },
    
        // Internal method called every time a model in the set fires an event.
        // Sets need to update their indexes when models change ids. All other
        // events simply proxy through. "add" and "remove" events that originate
        // in other collections are ignored.
        _onModelEvent: function(event, model, collection, options) {
          if (model) {
            if ((event === 'add' || event === 'remove') && collection !== this) return;
            if (event === 'destroy') this.remove(model, options);
            if (event === 'change') {
              var prevId = this.modelId(model.previousAttributes());
              var id = this.modelId(model.attributes);
              if (prevId !== id) {
                if (prevId != null) delete this._byId[prevId];
                if (id != null) this._byId[id] = model;
              }
            }
          }
          this.trigger.apply(this, arguments);
        }
    
      });
    
      // Defining an @@iterator method implements JavaScript's Iterable protocol.
      // In modern ES2015 browsers, this value is found at Symbol.iterator.
      /* global Symbol */
      var $$iterator = typeof Symbol === 'function' && Symbol.iterator;
      if ($$iterator) {
        Collection.prototype[$$iterator] = Collection.prototype.values;
      }
    
      // CollectionIterator
      // ------------------
    
      // A CollectionIterator implements JavaScript's Iterator protocol, allowing the
      // use of `for of` loops in modern browsers and interoperation between
      // Backbone.Collection and other JavaScript functions and third-party libraries
      // which can operate on Iterables.
      var CollectionIterator = function(collection, kind) {
        this._collection = collection;
        this._kind = kind;
        this._index = 0;
      };
    
      // This "enum" defines the three possible kinds of values which can be emitted
      // by a CollectionIterator that correspond to the values(), keys() and entries()
      // methods on Collection, respectively.
      var ITERATOR_VALUES = 1;
      var ITERATOR_KEYS = 2;
      var ITERATOR_KEYSVALUES = 3;
    
      // All Iterators should themselves be Iterable.
      if ($$iterator) {
        CollectionIterator.prototype[$$iterator] = function() {
          return this;
        };
      }
    
      CollectionIterator.prototype.next = function() {
        if (this._collection) {
    
          // Only continue iterating if the iterated collection is long enough.
          if (this._index < this._collection.length) {
            var model = this._collection.at(this._index);
            this._index++;
    
            // Construct a value depending on what kind of values should be iterated.
            var value;
            if (this._kind === ITERATOR_VALUES) {
              value = model;
            } else {
              var id = this._collection.modelId(model.attributes);
              if (this._kind === ITERATOR_KEYS) {
                value = id;
              } else { // ITERATOR_KEYSVALUES
                value = [id, model];
              }
            }
            return {value: value, done: false};
          }
    
          // Once exhausted, remove the reference to the collection so future
          // calls to the next method always return done.
          this._collection = void 0;
        }
    
        return {value: void 0, done: true};
      };
    
      // Backbone.View
      // -------------
    
      // Backbone Views are almost more convention than they are actual code. A View
      // is simply a JavaScript object that represents a logical chunk of UI in the
      // DOM. This might be a single item, an entire list, a sidebar or panel, or
      // even the surrounding frame which wraps your whole app. Defining a chunk of
      // UI as a **View** allows you to define your DOM events declaratively, without
      // having to worry about render order ... and makes it easy for the view to
      // react to specific changes in the state of your models.
    
      // Creating a Backbone.View creates its initial element outside of the DOM,
      // if an existing element is not provided...
      var View = Backbone.View = function(options) {
        this.cid = _.uniqueId('view');
        this.preinitialize.apply(this, arguments);
        _.extend(this, _.pick(options, viewOptions));
        this._ensureElement();
        this.initialize.apply(this, arguments);
      };
    
      // Cached regex to split keys for `delegate`.
      var delegateEventSplitter = /^(\S+)\s*(.*)$/;
    
      // List of view options to be set as properties.
      var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];
    
      // Set up all inheritable **Backbone.View** properties and methods.
      _.extend(View.prototype, Events, {
    
        // The default `tagName` of a View's element is `"div"`.
        tagName: 'div',
    
        // jQuery delegate for element lookup, scoped to DOM elements within the
        // current view. This should be preferred to global lookups where possible.
        $: function(selector) {
          return this.$el.find(selector);
        },
    
        // preinitialize is an empty function by default. You can override it with a function
        // or object.  preinitialize will run before any instantiation logic is run in the View
        preinitialize: function(){},
    
        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},
    
        // **render** is the core function that your view should override, in order
        // to populate its element (`this.el`), with the appropriate HTML. The
        // convention is for **render** to always return `this`.
        render: function() {
          return this;
        },
    
        // Remove this view by taking the element out of the DOM, and removing any
        // applicable Backbone.Events listeners.
        remove: function() {
          this._removeElement();
          this.stopListening();
          return this;
        },
    
        // Remove this view's element from the document and all event listeners
        // attached to it. Exposed for subclasses using an alternative DOM
        // manipulation API.
        _removeElement: function() {
          this.$el.remove();
        },
    
        // Change the view's element (`this.el` property) and re-delegate the
        // view's events on the new element.
        setElement: function(element) {
          this.undelegateEvents();
          this._setElement(element);
          this.delegateEvents();
          return this;
        },
    
        // Creates the `this.el` and `this.$el` references for this view using the
        // given `el`. `el` can be a CSS selector or an HTML string, a jQuery
        // context or an element. Subclasses can override this to utilize an
        // alternative DOM manipulation API and are only required to set the
        // `this.el` property.
        _setElement: function(el) {
          this.$el = el instanceof Backbone.$ ? el : Backbone.$(el);
          this.el = this.$el[0];
        },
    
        // Set callbacks, where `this.events` is a hash of
        //
        // *{"event selector": "callback"}*
        //
        //     {
        //       'mousedown .title':  'edit',
        //       'click .button':     'save',
        //       'click .open':       function(e) { ... }
        //     }
        //
        // pairs. Callbacks will be bound to the view, with `this` set properly.
        // Uses event delegation for efficiency.
        // Omitting the selector binds the event to `this.el`.
        delegateEvents: function(events) {
          events || (events = _.result(this, 'events'));
          if (!events) return this;
          this.undelegateEvents();
          for (var key in events) {
            var method = events[key];
            if (!_.isFunction(method)) method = this[method];
            if (!method) continue;
            var match = key.match(delegateEventSplitter);
            this.delegate(match[1], match[2], method.bind(this));
          }
          return this;
        },
    
        // Add a single event listener to the view's element (or a child element
        // using `selector`). This only works for delegate-able events: not `focus`,
        // `blur`, and not `change`, `submit`, and `reset` in Internet Explorer.
        delegate: function(eventName, selector, listener) {
          this.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
          return this;
        },
    
        // Clears all callbacks previously bound to the view by `delegateEvents`.
        // You usually don't need to use this, but may wish to if you have multiple
        // Backbone views attached to the same DOM element.
        undelegateEvents: function() {
          if (this.$el) this.$el.off('.delegateEvents' + this.cid);
          return this;
        },
    
        // A finer-grained `undelegateEvents` for removing a single delegated event.
        // `selector` and `listener` are both optional.
        undelegate: function(eventName, selector, listener) {
          this.$el.off(eventName + '.delegateEvents' + this.cid, selector, listener);
          return this;
        },
    
        // Produces a DOM element to be assigned to your view. Exposed for
        // subclasses using an alternative DOM manipulation API.
        _createElement: function(tagName) {
          return document.createElement(tagName);
        },
    
        // Ensure that the View has a DOM element to render into.
        // If `this.el` is a string, pass it through `$()`, take the first
        // matching element, and re-assign it to `el`. Otherwise, create
        // an element from the `id`, `className` and `tagName` properties.
        _ensureElement: function() {
          if (!this.el) {
            var attrs = _.extend({}, _.result(this, 'attributes'));
            if (this.id) attrs.id = _.result(this, 'id');
            if (this.className) attrs['class'] = _.result(this, 'className');
            this.setElement(this._createElement(_.result(this, 'tagName')));
            this._setAttributes(attrs);
          } else {
            this.setElement(_.result(this, 'el'));
          }
        },
    
        // Set attributes from a hash on this view's element.  Exposed for
        // subclasses using an alternative DOM manipulation API.
        _setAttributes: function(attributes) {
          this.$el.attr(attributes);
        }
    
      });
    
      // Proxy Backbone class methods to Underscore functions, wrapping the model's
      // `attributes` object or collection's `models` array behind the scenes.
      //
      // collection.filter(function(model) { return model.get('age') > 10 });
      // collection.each(this.addView);
      //
      // `Function#apply` can be slow so we use the method's arg count, if we know it.
      var addMethod = function(base, length, method, attribute) {
        switch (length) {
          case 1: return function() {
            return base[method](this[attribute]);
          };
          case 2: return function(value) {
            return base[method](this[attribute], value);
          };
          case 3: return function(iteratee, context) {
            return base[method](this[attribute], cb(iteratee, this), context);
          };
          case 4: return function(iteratee, defaultVal, context) {
            return base[method](this[attribute], cb(iteratee, this), defaultVal, context);
          };
          default: return function() {
            var args = slice.call(arguments);
            args.unshift(this[attribute]);
            return base[method].apply(base, args);
          };
        }
      };
    
      var addUnderscoreMethods = function(Class, base, methods, attribute) {
        _.each(methods, function(length, method) {
          if (base[method]) Class.prototype[method] = addMethod(base, length, method, attribute);
        });
      };
    
      // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
      var cb = function(iteratee, instance) {
        if (_.isFunction(iteratee)) return iteratee;
        if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
        if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
        return iteratee;
      };
      var modelMatcher = function(attrs) {
        var matcher = _.matches(attrs);
        return function(model) {
          return matcher(model.attributes);
        };
      };
    
      // Underscore methods that we want to implement on the Collection.
      // 90% of the core usefulness of Backbone Collections is actually implemented
      // right here:
      var collectionMethods = {forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
          foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
          select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
          contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
          head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
          without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
          isEmpty: 1, chain: 1, sample: 3, partition: 3, groupBy: 3, countBy: 3,
          sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
    
    
      // Underscore methods that we want to implement on the Model, mapped to the
      // number of arguments they take.
      var modelMethods = {keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
          omit: 0, chain: 1, isEmpty: 1};
    
      // Mix in each Underscore method as a proxy to `Collection#models`.
    
      _.each([
        [Collection, collectionMethods, 'models'],
        [Model, modelMethods, 'attributes']
      ], function(config) {
        var Base = config[0],
            methods = config[1],
            attribute = config[2];
    
        Base.mixin = function(obj) {
          var mappings = _.reduce(_.functions(obj), function(memo, name) {
            memo[name] = 0;
            return memo;
          }, {});
          addUnderscoreMethods(Base, obj, mappings, attribute);
        };
    
        addUnderscoreMethods(Base, _, methods, attribute);
      });
    
      // Backbone.sync
      // -------------
    
      // Override this function to change the manner in which Backbone persists
      // models to the server. You will be passed the type of request, and the
      // model in question. By default, makes a RESTful Ajax request
      // to the model's `url()`. Some possible customizations could be:
      //
      // * Use `setTimeout` to batch rapid-fire updates into a single request.
      // * Send up the models as XML instead of JSON.
      // * Persist models via WebSockets instead of Ajax.
      //
      // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
      // as `POST`, with a `_method` parameter containing the true HTTP method,
      // as well as all requests with the body as `application/x-www-form-urlencoded`
      // instead of `application/json` with the model in a param named `model`.
      // Useful when interfacing with server-side languages like **PHP** that make
      // it difficult to read the body of `PUT` requests.
      Backbone.sync = function(method, model, options) {
        var type = methodMap[method];
    
        // Default options, unless specified.
        _.defaults(options || (options = {}), {
          emulateHTTP: Backbone.emulateHTTP,
          emulateJSON: Backbone.emulateJSON
        });
    
        // Default JSON-request options.
        var params = {type: type, dataType: 'json'};
    
        // Ensure that we have a URL.
        if (!options.url) {
          params.url = _.result(model, 'url') || urlError();
        }
    
        // Ensure that we have the appropriate request data.
        if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
          params.contentType = 'application/json';
          params.data = JSON.stringify(options.attrs || model.toJSON(options));
        }
    
        // For older servers, emulate JSON by encoding the request into an HTML-form.
        if (options.emulateJSON) {
          params.contentType = 'application/x-www-form-urlencoded';
          params.data = params.data ? {model: params.data} : {};
        }
    
        // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
        // And an `X-HTTP-Method-Override` header.
        if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
          params.type = 'POST';
          if (options.emulateJSON) params.data._method = type;
          var beforeSend = options.beforeSend;
          options.beforeSend = function(xhr) {
            xhr.setRequestHeader('X-HTTP-Method-Override', type);
            if (beforeSend) return beforeSend.apply(this, arguments);
          };
        }
    
        // Don't process data on a non-GET request.
        if (params.type !== 'GET' && !options.emulateJSON) {
          params.processData = false;
        }
    
        // Pass along `textStatus` and `errorThrown` from jQuery.
        var error = options.error;
        options.error = function(xhr, textStatus, errorThrown) {
          options.textStatus = textStatus;
          options.errorThrown = errorThrown;
          if (error) error.call(options.context, xhr, textStatus, errorThrown);
        };
    
        // Make the request, allowing the user to override any Ajax options.
        var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
        model.trigger('request', model, xhr, options);
        return xhr;
      };
    
      // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
      var methodMap = {
        'create': 'POST',
        'update': 'PUT',
        'patch': 'PATCH',
        'delete': 'DELETE',
        'read': 'GET'
      };
    
      // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
      // Override this if you'd like to use a different library.
      Backbone.ajax = function() {
        return Backbone.$.ajax.apply(Backbone.$, arguments);
      };
    
      // Backbone.Router
      // ---------------
    
      // Routers map faux-URLs to actions, and fire events when routes are
      // matched. Creating a new one sets its `routes` hash, if not set statically.
      var Router = Backbone.Router = function(options) {
        options || (options = {});
        this.preinitialize.apply(this, arguments);
        if (options.routes) this.routes = options.routes;
        this._bindRoutes();
        this.initialize.apply(this, arguments);
      };
    
      // Cached regular expressions for matching named param parts and splatted
      // parts of route strings.
      var optionalParam = /\((.*?)\)/g;
      var namedParam    = /(\(\?)?:\w+/g;
      var splatParam    = /\*\w+/g;
      var escapeRegExp  = /[\-{}\[\]+?.,\\\^$|#\s]/g;
    
      // Set up all inheritable **Backbone.Router** properties and methods.
      _.extend(Router.prototype, Events, {
    
        // preinitialize is an empty function by default. You can override it with a function
        // or object.  preinitialize will run before any instantiation logic is run in the Router.
        preinitialize: function(){},
    
        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},
    
        // Manually bind a single named route to a callback. For example:
        //
        //     this.route('search/:query/p:num', 'search', function(query, num) {
        //       ...
        //     });
        //
        route: function(route, name, callback) {
          if (!_.isRegExp(route)) route = this._routeToRegExp(route);
          if (_.isFunction(name)) {
            callback = name;
            name = '';
          }
          if (!callback) callback = this[name];
          var router = this;
          Backbone.history.route(route, function(fragment) {
            var args = router._extractParameters(route, fragment);
            if (router.execute(callback, args, name) !== false) {
              router.trigger.apply(router, ['route:' + name].concat(args));
              router.trigger('route', name, args);
              Backbone.history.trigger('route', router, name, args);
            }
          });
          return this;
        },
    
        // Execute a route handler with the provided parameters.  This is an
        // excellent place to do pre-route setup or post-route cleanup.
        execute: function(callback, args, name) {
          if (callback) callback.apply(this, args);
        },
    
        // Simple proxy to `Backbone.history` to save a fragment into the history.
        navigate: function(fragment, options) {
          Backbone.history.navigate(fragment, options);
          return this;
        },
    
        // Bind all defined routes to `Backbone.history`. We have to reverse the
        // order of the routes here to support behavior where the most general
        // routes can be defined at the bottom of the route map.
        _bindRoutes: function() {
          if (!this.routes) return;
          this.routes = _.result(this, 'routes');
          var route, routes = _.keys(this.routes);
          while ((route = routes.pop()) != null) {
            this.route(route, this.routes[route]);
          }
        },
    
        // Convert a route string into a regular expression, suitable for matching
        // against the current location hash.
        _routeToRegExp: function(route) {
          route = route.replace(escapeRegExp, '\\$&')
                       .replace(optionalParam, '(?:$1)?')
                       .replace(namedParam, function(match, optional) {
                         return optional ? match : '([^/?]+)';
                       })
                       .replace(splatParam, '([^?]*?)');
          return new RegExp('^' + route + '(?:\\?([\\s\\S]*))?$');
        },
    
        // Given a route, and a URL fragment that it matches, return the array of
        // extracted decoded parameters. Empty or unmatched parameters will be
        // treated as `null` to normalize cross-browser behavior.
        _extractParameters: function(route, fragment) {
          var params = route.exec(fragment).slice(1);
          return _.map(params, function(param, i) {
            // Don't decode the search params.
            if (i === params.length - 1) return param || null;
            return param ? decodeURIComponent(param) : null;
          });
        }
    
      });
    
      // Backbone.History
      // ----------------
    
      // Handles cross-browser history management, based on either
      // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
      // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
      // and URL fragments. If the browser supports neither (old IE, natch),
      // falls back to polling.
      var History = Backbone.History = function() {
        this.handlers = [];
        this.checkUrl = this.checkUrl.bind(this);
    
        // Ensure that `History` can be used outside of the browser.
        if (typeof window !== 'undefined') {
          this.location = window.location;
          this.history = window.history;
        }
      };
    
      // Cached regex for stripping a leading hash/slash and trailing space.
      var routeStripper = /^[#\/]|\s+$/g;
    
      // Cached regex for stripping leading and trailing slashes.
      var rootStripper = /^\/+|\/+$/g;
    
      // Cached regex for stripping urls of hash.
      var pathStripper = /#.*$/;
    
      // Has the history handling already been started?
      History.started = false;
    
      // Set up all inheritable **Backbone.History** properties and methods.
      _.extend(History.prototype, Events, {
    
        // The default interval to poll for hash changes, if necessary, is
        // twenty times a second.
        interval: 50,
    
        // Are we at the app root?
        atRoot: function() {
          var path = this.location.pathname.replace(/[^\/]$/, '$&/');
          return path === this.root && !this.getSearch();
        },
    
        // Does the pathname match the root?
        matchRoot: function() {
          var path = this.decodeFragment(this.location.pathname);
          var rootPath = path.slice(0, this.root.length - 1) + '/';
          return rootPath === this.root;
        },
    
        // Unicode characters in `location.pathname` are percent encoded so they're
        // decoded for comparison. `%25` should not be decoded since it may be part
        // of an encoded parameter.
        decodeFragment: function(fragment) {
          return decodeURI(fragment.replace(/%25/g, '%2525'));
        },
    
        // In IE6, the hash fragment and search params are incorrect if the
        // fragment contains `?`.
        getSearch: function() {
          var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
          return match ? match[0] : '';
        },
    
        // Gets the true hash value. Cannot use location.hash directly due to bug
        // in Firefox where location.hash will always be decoded.
        getHash: function(window) {
          var match = (window || this).location.href.match(/#(.*)$/);
          return match ? match[1] : '';
        },
    
        // Get the pathname and search params, without the root.
        getPath: function() {
          var path = this.decodeFragment(
            this.location.pathname + this.getSearch()
          ).slice(this.root.length - 1);
          return path.charAt(0) === '/' ? path.slice(1) : path;
        },
    
        // Get the cross-browser normalized URL fragment from the path or hash.
        getFragment: function(fragment) {
          if (fragment == null) {
            if (this._usePushState || !this._wantsHashChange) {
              fragment = this.getPath();
            } else {
              fragment = this.getHash();
            }
          }
          return fragment.replace(routeStripper, '');
        },
    
        // Start the hash change handling, returning `true` if the current URL matches
        // an existing route, and `false` otherwise.
        start: function(options) {
          if (History.started) throw new Error('Backbone.history has already been started');
          History.started = true;
    
          // Figure out the initial configuration. Do we need an iframe?
          // Is pushState desired ... is it available?
          this.options          = _.extend({root: '/'}, this.options, options);
          this.root             = this.options.root;
          this._wantsHashChange = this.options.hashChange !== false;
          this._hasHashChange   = 'onhashchange' in window && (document.documentMode === void 0 || document.documentMode > 7);
          this._useHashChange   = this._wantsHashChange && this._hasHashChange;
          this._wantsPushState  = !!this.options.pushState;
          this._hasPushState    = !!(this.history && this.history.pushState);
          this._usePushState    = this._wantsPushState && this._hasPushState;
          this.fragment         = this.getFragment();
    
          // Normalize root to always include a leading and trailing slash.
          this.root = ('/' + this.root + '/').replace(rootStripper, '/');
    
          // Transition from hashChange to pushState or vice versa if both are
          // requested.
          if (this._wantsHashChange && this._wantsPushState) {
    
            // If we've started off with a route from a `pushState`-enabled
            // browser, but we're currently in a browser that doesn't support it...
            if (!this._hasPushState && !this.atRoot()) {
              var rootPath = this.root.slice(0, -1) || '/';
              this.location.replace(rootPath + '#' + this.getPath());
              // Return immediately as browser will do redirect to new url
              return true;
    
            // Or if we've started out with a hash-based route, but we're currently
            // in a browser where it could be `pushState`-based instead...
            } else if (this._hasPushState && this.atRoot()) {
              this.navigate(this.getHash(), {replace: true});
            }
    
          }
    
          // Proxy an iframe to handle location events if the browser doesn't
          // support the `hashchange` event, HTML5 history, or the user wants
          // `hashChange` but not `pushState`.
          if (!this._hasHashChange && this._wantsHashChange && !this._usePushState) {
            this.iframe = document.createElement('iframe');
            this.iframe.src = 'javascript:0';
            this.iframe.style.display = 'none';
            this.iframe.tabIndex = -1;
            var body = document.body;
            // Using `appendChild` will throw on IE < 9 if the document is not ready.
            var iWindow = body.insertBefore(this.iframe, body.firstChild).contentWindow;
            iWindow.document.open();
            iWindow.document.close();
            iWindow.location.hash = '#' + this.fragment;
          }
    
          // Add a cross-platform `addEventListener` shim for older browsers.
          var addEventListener = window.addEventListener || function(eventName, listener) {
            return attachEvent('on' + eventName, listener);
          };
    
          // Depending on whether we're using pushState or hashes, and whether
          // 'onhashchange' is supported, determine how we check the URL state.
          if (this._usePushState) {
            addEventListener('popstate', this.checkUrl, false);
          } else if (this._useHashChange && !this.iframe) {
            addEventListener('hashchange', this.checkUrl, false);
          } else if (this._wantsHashChange) {
            this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
          }
    
          if (!this.options.silent) return this.loadUrl();
        },
    
        // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
        // but possibly useful for unit testing Routers.
        stop: function() {
          // Add a cross-platform `removeEventListener` shim for older browsers.
          var removeEventListener = window.removeEventListener || function(eventName, listener) {
            return detachEvent('on' + eventName, listener);
          };
    
          // Remove window listeners.
          if (this._usePushState) {
            removeEventListener('popstate', this.checkUrl, false);
          } else if (this._useHashChange && !this.iframe) {
            removeEventListener('hashchange', this.checkUrl, false);
          }
    
          // Clean up the iframe if necessary.
          if (this.iframe) {
            document.body.removeChild(this.iframe);
            this.iframe = null;
          }
    
          // Some environments will throw when clearing an undefined interval.
          if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
          History.started = false;
        },
    
        // Add a route to be tested when the fragment changes. Routes added later
        // may override previous routes.
        route: function(route, callback) {
          this.handlers.unshift({route: route, callback: callback});
        },
    
        // Checks the current URL to see if it has changed, and if it has,
        // calls `loadUrl`, normalizing across the hidden iframe.
        checkUrl: function(e) {
          var current = this.getFragment();
    
          // If the user pressed the back button, the iframe's hash will have
          // changed and we should use that for comparison.
          if (current === this.fragment && this.iframe) {
            current = this.getHash(this.iframe.contentWindow);
          }
    
          if (current === this.fragment) return false;
          if (this.iframe) this.navigate(current);
          this.loadUrl();
        },
    
        // Attempt to load the current URL fragment. If a route succeeds with a
        // match, returns `true`. If no defined routes matches the fragment,
        // returns `false`.
        loadUrl: function(fragment) {
          // If the root doesn't match, no routes can match either.
          if (!this.matchRoot()) return false;
          fragment = this.fragment = this.getFragment(fragment);
          return _.some(this.handlers, function(handler) {
            if (handler.route.test(fragment)) {
              handler.callback(fragment);
              return true;
            }
          });
        },
    
        // Save a fragment into the hash history, or replace the URL state if the
        // 'replace' option is passed. You are responsible for properly URL-encoding
        // the fragment in advance.
        //
        // The options object can contain `trigger: true` if you wish to have the
        // route callback be fired (not usually desirable), or `replace: true`, if
        // you wish to modify the current URL without adding an entry to the history.
        navigate: function(fragment, options) {
          if (!History.started) return false;
          if (!options || options === true) options = {trigger: !!options};
    
          // Normalize the fragment.
          fragment = this.getFragment(fragment || '');
    
          // Don't include a trailing slash on the root.
          var rootPath = this.root;
          if (fragment === '' || fragment.charAt(0) === '?') {
            rootPath = rootPath.slice(0, -1) || '/';
          }
          var url = rootPath + fragment;
    
          // Strip the fragment of the query and hash for matching.
          fragment = fragment.replace(pathStripper, '');
    
          // Decode for matching.
          var decodedFragment = this.decodeFragment(fragment);
    
          if (this.fragment === decodedFragment) return;
          this.fragment = decodedFragment;
    
          // If pushState is available, we use it to set the fragment as a real URL.
          if (this._usePushState) {
            this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
    
          // If hash changes haven't been explicitly disabled, update the hash
          // fragment to store history.
          } else if (this._wantsHashChange) {
            this._updateHash(this.location, fragment, options.replace);
            if (this.iframe && fragment !== this.getHash(this.iframe.contentWindow)) {
              var iWindow = this.iframe.contentWindow;
    
              // Opening and closing the iframe tricks IE7 and earlier to push a
              // history entry on hash-tag change.  When replace is true, we don't
              // want this.
              if (!options.replace) {
                iWindow.document.open();
                iWindow.document.close();
              }
    
              this._updateHash(iWindow.location, fragment, options.replace);
            }
    
          // If you've told us that you explicitly don't want fallback hashchange-
          // based history, then `navigate` becomes a page refresh.
          } else {
            return this.location.assign(url);
          }
          if (options.trigger) return this.loadUrl(fragment);
        },
    
        // Update the hash location, either replacing the current entry, or adding
        // a new one to the browser history.
        _updateHash: function(location, fragment, replace) {
          if (replace) {
            var href = location.href.replace(/(javascript:|#).*$/, '');
            location.replace(href + '#' + fragment);
          } else {
            // Some browsers require that `hash` contains a leading #.
            location.hash = '#' + fragment;
          }
        }
    
      });
    
      // Create the default Backbone.history.
      Backbone.history = new History;
    
      // Helpers
      // -------
    
      // Helper function to correctly set up the prototype chain for subclasses.
      // Similar to `goog.inherits`, but uses a hash of prototype properties and
      // class properties to be extended.
      var extend = function(protoProps, staticProps) {
        var parent = this;
        var child;
    
        // The constructor function for the new subclass is either defined by you
        // (the "constructor" property in your `extend` definition), or defaulted
        // by us to simply call the parent constructor.
        if (protoProps && _.has(protoProps, 'constructor')) {
          child = protoProps.constructor;
        } else {
          child = function(){ return parent.apply(this, arguments); };
        }
    
        // Add static properties to the constructor function, if supplied.
        _.extend(child, parent, staticProps);
    
        // Set the prototype chain to inherit from `parent`, without calling
        // `parent`'s constructor function and add the prototype properties.
        child.prototype = _.create(parent.prototype, protoProps);
        child.prototype.constructor = child;
    
        // Set a convenience property in case the parent's prototype is needed
        // later.
        child.__super__ = parent.prototype;
    
        return child;
      };
    
      // Set up inheritance for the model, collection, router, view and history.
      Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;
    
      // Throw an error when a URL is needed, and none is supplied.
      var urlError = function() {
        throw new Error('A "url" property or function must be specified');
      };
    
      // Wrap an optional error callback with a fallback error event.
      var wrapError = function(model, options) {
        var error = options.error;
        options.error = function(resp) {
          if (error) error.call(options.context, model, resp, options);
          model.trigger('error', model, resp, options);
        };
      };
    
      return Backbone;
    });
    